1. Field of the Invention
The present invention relates to a composite electronic module in which a non-reciprocal circuit element is mounted on a substrate and to a method of manufacturing a composite electronic module.
2. Description of the Related Art
To date, non-reciprocal circuit elements, such as isolators and circulators, have been used in composite electronic modules, such as power amplifier modules, of transmission circuit units of communication terminals, such as cellular phones and wireless LAN devices, by utilizing their characteristic of transmitting a signal only in a specific predetermined direction. A non-reciprocal circuit element 500, which is mounted on a substrate that defines a portion of this type of composite electronic module, for example, as illustrated in FIGS. 11A and 11B, includes a ferrite 505 that is sandwiched between a pair of substantially rectangular-parallelepiped-shaped permanent magnets 501 on which central electrodes 503 and 504, which are electrically insulated from each other, are provided on main surfaces 502 of the permanent magnets 501 (refer to, for example, Japanese Unexamined Patent Application Publication No. 2006-311455 (paragraphs [0019] to [0033], FIGS. 1, 2 etc.), Japanese Unexamined Patent Application Publication No. 2007-208943 (paragraphs [0016] to [0037], FIGS. 1, 2, etc.) and Japanese Unexamined Patent Application Publication No. 2009-49879 (paragraphs [0013] to [0032], FIGS. 1, 2, etc.)).
In addition, the ferrite 505 has a substantially rectangular parallelepiped shape and includes relay electrodes 506, which are for respectively electrically connecting the central electrodes 503 and 504 provided on one of the permanent magnets 501 to the central electrodes 503 and 504 provided on the other of the permanent magnets 501, are provided on the surfaces of the upper edge and the lower edge of the ferrite 505. By configuring the non-reciprocal circuit element 500 in this manner, as compared to the configuration of a conventional non-reciprocal circuit element in which a ferrite, around which a copper wire is wound to define as a central electrode, is positioned between a pair of permanent magnets, the non-reciprocal circuit element 500 is easier to manufacture and it is possible to reduce the size of the non-reciprocal circuit element 500. In order to suppress the effect of the magnetic field generated by the permanent magnets 501, a variety of composite electronic modules have been provided, in which the non-reciprocal circuit element 500 has been mounted on a substrate together with a metal yoke that functions as an electromagnetic shield. FIGS. 11A and 11B respectively illustrate an exploded perspective view and a perspective view of an example of the conventional non-reciprocal circuit element 500.
In recent years, together with communication terminals becoming smaller and thinner, a reduction of the size and profile of various composite electronic modules that are mounted in such communication terminals has also been demanded. Accordingly, in order to reduce the size and profile of composite electronic modules, formation of a composite electronic module by mounting the non-reciprocal circuit element 500 on a substrate while omitting a yoke has been considered. If such a configuration is used, since there is no need to provide a space on the substrate in which to mount a yoke, the size and profile of the composite electronic module can be reduced.
However, in this case, since a yoke that would function as an electromagnetic shield is not mounted on the substrate, at the time of forming the composite electronic module, when the non-reciprocal circuit element 500 and an electronic component that includes a magnetic material are mounted together on a substrate, there is risk of the electronic component, which is mounted around the periphery of the non-reciprocal circuit element 500, being shifted by the magnetic force of the permanent magnets 501 and thereby being displaced. Thus, the prevention of such displacement has been demanded.